U.S. patent number 3,909,536 [Application Number 05/467,267] was granted by the patent office on 1975-09-30 for audience survey system.
This patent grant is currently assigned to Northern Electric Company Limited. Invention is credited to Peter Parkinson, Douglas John Watson.
United States Patent |
3,909,536 |
Watson , et al. |
September 30, 1975 |
Audience survey system
Abstract
An incasting system which makes possible an interactive
participative broadcasting system is described. A plurality of
incasting signal generators are each located at respective ones of
a plurality of sources which are connected to a central sink via
respective communication paths. Detector means located at the
central sink are each responsive to the signal which may appear on
any one of a plurality of the communication paths.
Inventors: |
Watson; Douglas John (Ottawa,
CA), Parkinson; Peter (Ottawa, CA) |
Assignee: |
Northern Electric Company
Limited (Montreal, CA)
|
Family
ID: |
23855042 |
Appl.
No.: |
05/467,267 |
Filed: |
May 6, 1974 |
Current U.S.
Class: |
379/92.03;
455/2.01 |
Current CPC
Class: |
H04M
11/06 (20130101) |
Current International
Class: |
H04M
11/06 (20060101); H04M 011/06 () |
Field of
Search: |
;179/2AS,1AT,18F ;325/31
;178/DIG.13 ;340/253P |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Claffy; Kathleen H.
Assistant Examiner: Bartz; C. T.
Attorney, Agent or Firm: Turpin; Frank
Claims
What is claimed is:
1. An incasting communication system comprising:
a plurality of distributed sources;
a central sink;
a plurality of communication paths for connecting said sources to
said sink;
means located at each of said sources for generating and
transmitting on a respective one of the paths a signal having
predetermined characteristics; and
means located at the sink for detecting the presence of said signal
on any one of a plurality of said communication paths, said
detector means being concurrently connected to said plurality of
communication paths.
2. An incasting communication system using the telephone network
for the transmission of signals from distributed sources to a
central sink, comprising:
means located at each of said distributed sources for generating
and transmitting on respective subscriber telephone lines a signal
having predetermined characteristics; and
means located at the central sink for detecting the presence of
said signals, said detector means being connected to a plurality of
said telephone lines.
3. An incasting system using the telephone network for the
transmission of signals from subscriber terminals to a central
office, comprising:
signal generator means located at each of said subscriber terminals
for generating and transmitting on a respective telephone line an
incast signal having predetermined characteristics, said signal
generator means being connected across said respective telephone
line in parallel with its associated conventional telephone
subset;
detector means located at the central office for inductively
detecting the presence of said signal, said detector means being
connected to a plurality of said telephone lines and being
responsive to the signal appearing on any one of said plurality of
telephone lines for providing a corresponding output signal.
4. An incasting system as defined in claim 3 wherein said incast
signal comprises at least one current pulse having a predetermined
shape whereby a minimum of impulse noise is caused to be generated
and wherein said pulse is transmitted between one side of the
telephone line and ground.
5. An incasting system as defined in claim 4 wherein said signal
generator means comprises a capacitance element, a current pulse
generator and shaper, and switch means for connecting said
capacitance element through a high impedance to the tip and ring
leads of the subscriber loop in a first position, and for
connecting said capacitance element to ground and to one side of
the telephone line through said current pulse generator and shaper
in a second position, whereby said capacitance element charges up
in said first position and discharges through said current
generator and shaper in said second position to cause said current
pulse to be generated and transmitted on the line.
6. An incasting system as defined in claim 5 further comprising a
visual indicator serially connected between said signal generator
means and said one side of the telephone line for indicating that
said current pulse has been transmitted.
7. An incasting system as defined in claim 4 wherein said detector
means is a current sensing transformer comprising, a core of
magnetic material adapted to have a plurality of conductors passing
therethrough, each of said conductors forming a primary winding,
and a secondary winding comprising a plurality of turns of wire
wound about said core, said transformer being adapted to provide an
output signal on the output leads of said secondary winding in
response to said current pulse passing through at least one of said
conductors.
8. An incasting system as defined in claim 7 wherein the secondary
winding of the transformer is divided in two halves, each half
comprising a plurality of turns of wire wound about a respective
portion of the core and the two halves being connected in series
aiding for the desired signal.
9. An incasting system as defined in claim 8 wherein said detector
means further includes a damping circuit comprising a parallel
circuit of a resistance element and a capacitance element connected
across the output leads of the secondary winding of the
transformer.
10. An incasting system using the telephone network for the
transmission of signals from distributed sources to a central
source, comprising:
signal generator means located at each of said distributed sources
for generating and transmitting on a respective telephone line a
signal having predetermined characteristics;
detector means located at the central sink for inductively
detecting the presence of said signal, said detector means being
responsive to the signal appearing on any one of a plurality of
said telephone lines for providing a corresponding output signal;
and
circuit means responsive to said output signal for validating it as
to amplitude and identifying it as to polarity and for providing
corresponding signals to a totalizing circuit.
11. An incasting system as defined in claim 10 wherein said circuit
means comprises:
a differential amplifier having its input terminal connected to
receive said output signal from said detector means and a pair of
output terminals;
a pair of threshold circuits each having its input terminal
connected to a respective one of the output terminals of the
amplifier and a pair of output terminals for providing said
corresponding signals.
Description
This application relates generally to communication systems and
more particularly to an incasting system using the telephone
network.
The term incasting is used to describe the communications function
that is the opposite of broadcasting; that is, the inward flow of
information from many sources to a common destination.
Generally, communications is the conveyance of information from
sources to sinks. A first mode of communication may be described as
the flow of information from a single source to a single sink, for
example, a conversation between two individuals. A second mode of
communication is characterized by the flow of information from a
single source to many sinks. The term broadcasting may be employed
to define such a system whether the media of transmission is radio,
television or the post office (circulars, magazines, etc.).
Finally, the term incasting may be used to define the mode of
communication wherein the flow of information is from many sources
to a single sink.
The existing incasting services have been implemented using a
variety of techniques. Some systems use the call-in technique, i.e.
radio call-in programs and telethons, wherein a large number of
people call a central sink on a given signal. This causes the
central office where the sink is located to be immediately jammed
with calls and causes the majority of incasters to be blocked out.
Other systems which are used for political polls, television
ratings, consumer product surveys, etc., employ the call-out
technique whereby attendants call the participants and query them
on their vote. Since this technique is not automated, it is very
slow and can only be used where the number of participants is
limited. Finally, another technique uses automatic call-out, e.g.
meter reading wherein a sophisticated machine at a central office
interrogates transponders located on the subscriber's premises.
Such a system requires the continuous use of central office common
control equipment thereby decreasing its normal call handling
capacity. The latest technique to be developed also makes use of
the telephone network as the incasting communication system. The
responders are required to access the sink in the conventional
manner. The calls are switched to respective voice recognition
systems in accordance with the directory number dialled and the
reply is identified and registered. In addition to being very
expensive, this system suffers from the usual problems associated
with the use of the telephone system for functions other than
conventional service.
None of the existing incasting techniques provide the facility for
dialogue between the sink and the sources. For such a system to
exist, the speed of the incast must be approximately the same as
the speed of the broadcast. The achievement of that goal results in
the realization of the concept of interactive participative
broadcasting. That is, a poll directed at the public at large may
be conducted on radio and television and the answers returned to
the pollster in a matter of seconds.
It is a general object of this invention to provide an incasting
system which makes it possible to achieve an interactive
participative broadcasting system which provides for fast response,
and which is practical and economical. The prime requirement of
such a system is that a two-way communication system be available.
According to the invention, the broadcasting systems, e.g. radio
and television, provide a one-way communication path from the
pollster to the public while the telephone system, particularly the
subscriber loops, provides the return communication path to the
pollster.
The prior art incasting systems employ the telephone network in a
manner resembling its conventional mode of operation. That is,
there is a one-to-one relationship between the incast sources and
the sinks. A receiver or detector circuit is provided at the sink
for each subscriber loop on which an incast signal may appear. In
accordance with this invention, each detector circuit at the sink
is responsive to the incast signal appearing on any one of a
plurality of communication paths between the sources and the sink.
A detector means located at the central office inductively detects
the presence of incast signals on a plurality of lines and
therefore has no electrical contact with the subscriber loops. Its
installation requires no interruption of service and it cannot pick
up conversations on the telephone line, thereby insuring privacy to
the subscriber.
However, the use of the telephone subscriber loops for the
transmission of signals extraneous to the conventional use of the
telephone set presents serious problems if the normal operation of
the telephone system is not to be altered and the service degraded.
For example, the application of a pulsed signal to the subscriber
loop generates noise in that loop directly and in other loops by
crosstalk. Another problem is that the connection of a signal path
to ground at or near the end of a subscriber loop will enable
longitudinally induced voltages in the loop to cause current to
flow and thus result in undesired noise in the talking path. A
further problem is that the connection of any circuit element
between tip and ring, or between either and ground, of less than
several thousands of ohms equivalent direct current resistance will
cause failure indications to occur when that line is subjected to
automatic line insulation testing (ALIT).
The invention circumvents these problems by providing an incast
transmitter located at each of the incast sources for generating
and transmitting on a respective one of the communication paths, a
signal which has predetermined characteristics. The signal
comprises one or more current pulses shaped such that the
frequencies most likely to cause noise and crosstalk are
suppressed. The signal is controlled by a current regulator (which
inherently has a high internal a-c impedance). and is applied to
the telephone line between one side thereof and local ground.
The system of the invention also exhibits novel circuit techniques.
The incast signal generator is loop powered and presents a very
high impedance to the loop at all times thereby preventing loading
of the subscriber loops. The signal generator may also be provided
with circuit means to prevent multiple responses on the same
question and to inhibit the generation of noise on the telephone
line due to "playing" with the reply key. In addition, the
generator may provide visual feedback to the user to confirm that
the intended reply has been sent.
An example embodiment of the invention will now be described in
conjunction with the drawings in which:
FIG. 1 is a block diagram of an incasting system in accordance with
the invention;
FIG. 2 is a waveform diagram of the signal generated by the incast
signal generator circuit of FIG. 1;
FIG. 3 is a schematic diagram of the incast signal generator
circuit shown in FIG. 1;
FIG. 4 is a pictorial diagram of the detector shown in FIG. 1;
FIG. 5 is a diagram of the waveforms at the detector of FIG. 4;
and
FIG. 6 is a block diagram of the reply sorter circuit shown in FIG.
1.
FIG. 1 shows a plurality of subscriber telephone sets 10 each
connected to a respective subscriber loop 11. The subscriber loops
11 eventually form a cable 12 which is terminated on the verticals
of a main distributing frame (MDF) 13 in a central office 14. The
horizontals of the MDF are formed into cables (typically 100 pairs
each) for connection to the central office switching equipment. All
of the above apparatus is conventional equipment which is to be
found in any telephone system. This apparatus serves as the return
communication link for the incasting system of the present
invention.
An incast signal generator circuit 15 is connected to the telephone
line 11 in parallel with each telephone set 10. The signal
generator circuit 15 may be incorporated into the telephone set 10;
however, for practical reasons, it may ideally take the form of a
separate unit connected to the telephone line via an electrical
cable and a jack connector. In this way, the signal generator
circuit 15 may be placed in the home at a location proximate the
broadcast receiver, and/or the seating location of the
incaster.
As described further below in conjunction with FIGS. 2 and 3, the
signal generator circuit 15 is powered from the telephone line and
therefore requires only a pair of wires connected thereto in
addition to a connection to the local ground. Physically, the
circuit 15 may be a small hand-held box with a manually operated
switch means which allows the incaster to indicate a "yes" or "no"
reply. It may also be provided with a visual indicator which
informs the operator that the desired signal has been sent.
The wires coming out of the MDF 13 are typically formed into one
hundred pair cables 16 for connection to the switching equipment of
a central office. A detector means 17 is provided for each of these
cables. As illustrated in FIG. 1, the detector means 17 is adapted
to perform an "OR" logic function on the incast signals thereby
providing a 100-to-1 concentration thereof and reducing the
detector equipment cost by a factor corresponding to the number of
pairs in each cable 16 in comparison to using a detector means for
each subscriber loop.
The output signal from each of the detector means 17 is fed to a
respective reply sorter 18 which determines if the reply is
positive or negative, and which provides an output signal which may
be fed to a totalizer 19 from which the total number of positive
and negative replies may be transmitted to any destination using
conventional methods. The totalizer 10 may comprise any
conventional counting circuit such as are well known in the
art.
The incasting signal generator 15 is required to generate a
unipolar current pulse having a predetermined risetime and a
predetermined falltime whereby a minimum of impulse noise is caused
to be generated. FIG. 2 shows, in broken line, the current vs time
relationship of an ideal single unipolar current pulse which causes
very little disturbance to the telephone system and yet permits
satisfactory operation of this incasting system. The solid line
shows a near approximation to the idealized broken line curve and
it represents a pulse which may be generated using practical
circuitry.
As may be observed from FIG. 2, the pulse has a sloped risetime of
approximately 2 milliseconds and a peak value of approximately 20
milliamperes. From this peak value, the pulse falls towards ground
in approximately 50 milliseconds. Of course, these values only
serve to indicate the desired shape of the current pulse to be
generated by the circuit 15 in order that a minimum of noise
interference be generated.
FIG. 3 is a schematic diagram of the incasting signal generator
circuit 15 shown in FIG. 1. This circuit is adapted to produce the
waveform of FIG. 2 as a positive signal or a signal. The The latter
is simply the mirror image to that shown in FIG. 2. FIG. 3 shows a
key S having three sets of transfer contacts S-1, S-2 and S-3. Make
contacts Y and N correspond to positive and negative replies
respectively. Each of these sets of contacts may be mechanically
linked so that they operate in unison. However, contacts S-1 should
be late-make in the Y and N positions. In the center position, the
key S serves to connect a capacitor C1 to the ring and tip leads of
the subscriber loop 11 through resistances R1 and R2 and diodes D1
and D2. These resistances may have a large value (e.g. 120 kilohm
each) so that the signal generator 15 does not load the loop 11. In
the Y and N positions, the capacitor C1 is connected to the local
ground and to one side of the subscriber loop 11 through a current
pulse generator and shaper 30 and a visual indicator 31.
The visual indicator 31 may conveniently be a red-green
light-emitting diode package such as are commercially available.
When a positive-going current pulse is generated, the green diode
is energized and when a negative-going current pulse is generated,
the red diode is energized. This indicator informs the voter that
his reply has been sent and confirms the nature thereof.
The circuit of the current pulse generator and shaper 30 may be
best described by describing the operation of the circuit of FIG.
3. With the voting key S in the center position and with the
associated telephone set on-hook, capacitor C1 charges through
resistors R1 and R2 and diodes D1 and D2 from the central office
battery supply of -48 volts connected to the ring lead. Capacitor
C2 also charges up through these elements but its charging path
also includes diode D3 and zener diode ZD1 which allow capacitor C2
to charge only to the voltage reached across capacitor C1 less the
breakdown voltage of zener diode ZD1.
When the key S is operated to the Y or N positions, the capacitor
C1 is disconneced from across the loop 11 and is connected through
the shaping circuitry to the tip lead only and to the local ground
so that the generated positive or negative current pulse will be
applied to the tip lead. As the contacts of the key S close, a
positive start pulse is generated at the base of transister Q1, via
resistor dividing network R3 and R4, capacitors C2 and C3 and diode
ZD2. This pulse allows current to flow through Q1, part of which
flows through R5. A capacitor C4 charges at a predetermined rate
until diode D4 starts to conduct thereby holding the voltage at
that point to the value existing on capacitor C2. This voltage ramp
applied to the base of transistor Q2, and via the emitter of Q2 to
the base of transistor Q3, causes a current ramp of a predetermined
rate (in this embodiment, 10 milliamperes per millisecond, 20
milliamperes maximum) to be passed by the collector of transistor
Q3 due to the current feedback provided by emitter resistor R6. The
collector current of transistor Q2 is applied to resistor R7 and
the base of transistor Q1 to maintain it in a saturated "on"
condition after the decay of the start pulse. Capacitor C1 is now
discharging through resistor R6, transister Q3, the indicator 31
and the tip lead. The magnitude of the discharge current is
controlled by resistor R6 and the difference between the voltages
remaining on capacitors C1 and C2. Capacitor C2 is supplying a
small amount of current, hence its voltage remains approximately
constant. As shown in FIG. 2, the discharge current decays
exponentially and its decay time is dependent on the value chosen
for capacitor C1. In FIG. 2, the discharge rate is shown to be
about 10 milliamperes per 25 milliseconds. As the discharge current
approaches zero, the current through the collector of Q2 reduces,
causing transistor Q1 to come out of saturation and the output
current to switch to zero. This is shown as the small step at the
end of the pulse illustrated in FIG. 2.
It may be noted that diode ZD2 prevents the generation of noise on
the telephone line because of repeated operation ("playing with")
of the key S. Operating the reply key S does not trigger the
current pulse generator 30 until C1 has recharged enough to cause
C2 to charge to a voltage such that the trigger signal generated at
the junction of resistors R3 and R4 plus the voltage on capacitor
C2 is greater than the zener voltage of ZD2 plus the base-emitter
threshold voltage of transistor Q1.
FIG. 4 is a pictorial diagram of the detector 17 shown in FIG. 1 of
the drawings. There is shown a cross-sectional view of a current
sensing transformer 40 having a core 41 of magnetic material which
may be made of grain-oriented silicon steel tape. The core 41 may
be split in two sections and held together with a steel band 42 and
a fastening means 43 which may be a nut and bolt arrangement or any
other conventional fastening means. A pair of bobbins 44 mounted on
the core 41 carry a secondary winding comprising a large number of
turns of insulated conductor. As shown in the drawing, the
cross-sectional area 45 bounded by the bobbins 44 and the core 41
should be made just large enough to accommodate one of the cable 16
connecting the horizontals of the MDF 13 to the central office
switching equipment as shown in FIG. 1. Each pair of the cables
passing through the transformer 40 serves as a one-turn primary
winding whereas the windings on the bobbins 44 serve as the
secondary winding. A secondary winding wound on only one bobbin is
sufficient to obtain an output signal, however, it is preferable to
wind the secondary winding on two bobbins, as shown. because when
they are connected in series aiding for the desired output signal,
the voltages induced by external fields tend to cancel.
The operation of the transformer is as follows:
The number of magnetic lines of force (flux) in a transformer core
is given by: ##EQU1## .mu.= the magnetic permeability of the core
material, A = the cross-sectional area of the core,
n.sub.1 = the number of turns of wire,
I = current flowing in the wire
l = mean length of magnetic flux lines, and
K = proportionality constant.
Assuming no current flow in the secondary winding of the
transformer, the flux in the sensor core is directly proportional
to the current flow represented by the current pulse illustrated in
FIG. 2.
The voltage induced in the secondary winding is proportional to
(n.sub.2 d.phi./dt) where n.sub.2 = number of turns of wire in the
secondary winding. The differential of .phi. with respect to time,
(d.phi./d), represents the idealized output voltage from the sensor
terminals.
FIG. 5 shows the waveforms related to the transformer 40. The (a)
waveform represents the current pulse flowing through the tip lead
of one of the pairs of the cable 16 passing through the transformer
40. Waveform (b) represents the flux generated in the transformer
core 41 whereas waveform (c) shows the voltage waveform generated
at the output leads of the secondary winding. These waveforms are
related to a yes reply generated by the signal generator 15 of FIG.
1. For a no reply the direction of the signals shown in FIG. 6 is
reversed.
An important advantage of using a current pulse signalling system
such as that described above now becomes evident. The strength of
the received signal is independent of the subscriber loop impedance
-- at least within the conventional impedance range thereof. This
is because the pulse consists of a controlled current and what
varies, as the tip-to-ground impedance varies, is the voltage
generated at the current injection point.
Due to the self-capacitance of the secondary winding, resonance may
tend to occur and it may be necessary to terminate the sensor
terminals in a resistance R (FIG. 4) low enough to critically damp
the resultant oscillations. It may also be advantageous to
terminate the sensor with a capacitor C (FIG. 4) to lower the
resonant frequency of the combination and effectively use the
inductance of the secondary winding and these capacitances together
as a low pass filter to suppress at lease partially the noise that
appears at the sensor terminals.
FIG. 6 is a circuit block diagram of the vote sorter 18 shown in
FIG. 1, A differential amplifier 60 has its input connected to the
detector 16 of FIG. 1 and a pair of outputs each one connected to a
respective input of Schmitt trigger circuits 61 and 62. A bias
stabilization amplifier 63 is connected to the Schmitt trigger
circuits 61 and 62 to ensure that the positive and negative
thresholds thereof remain equal in magnitude. A current regulator
circuit 64 may be connected to the differential amplifier 60 to
ensure symmetrical operation thereof.
When a pulse from the detector 17 is applied to the vote sorter of
FIG. 6, the differential amplifier 60 directs it to the appropriate
threshold level circuit 61 or 62 which in turn provides a logic
pulse corresponding to the signal generated by the incast signal
generator 15 of FIG. 1. Thus, for each vote registered in a group
of subscriber loops (i.e. 100), a pulse appears at the yes output
for each yes reply and at the no output for each no reply.
OPERATION
As discussed previously, this system is envisaged as an incasting
system for use by anyone who has access to a telephone subscriber
loop. In response to a question transmitted over a broadcasting
facility such as radio or television, listeners and/or viewers are
given a predetermined period of time (e.g. 10 seconds) to register
their reply on the question asked. In response to the question, the
subscribers who wish to participate in the poll operate the key of
their signal generator 15 to the yes or no position, thereby
causing a current pulse representative of their reply to be
generated. This current pulse is applied to the tip lead of the
subscriber telephone loop and local ground and is received by
detector 17 located in the local central office. The detector 17
provides a signal to the reply sorter circuit 18 which in turn
generates a signal for use by a totalizer circuit 19. After the
allocated 10 seconds, the totalizer along with other conventional
transmission circuitry sends the result to the pollster. Because
the response time of this system is so fast, the answers from the
listeners and/or viewers can affect subsequent questioning.
As described above, each detector 17 responds to the signals which
may appear on any pair of its associated cable (100 pair cable). If
any two of these paths carry opposite signals (one yes reply and
one no reply) at exactly the same period in time, the signals
cancel out and those replies are not registered. However, it has
been found that both practically and statistically, this occurrence
is not a problem as it is very unlikely. There are a number of
reasons for this. The detector and reply sorter circuits provide a
signal to the totalizer in less than five milliseconds. Assuming a
ten seconds replying period, (which is minimal in view of typical
physical human response) there are 2,000 reply slots in which to
process a maximum of one hundred signals. Of course, this is
assuming that all of the pairs in the cable associated with any one
detector belong to subscribers who are all equipped with an incast
signal generator circuit and who are all watching the same
television program or all listening to the same radio program and
who all wish to participate.
This system provides a truly interactive participative broadcasting
system which is both practical and economical. Since it uses the
telephone subscriber loop network as the incasting communication
link it is available for use by almost everyone. The incast signal
generator circuit does not load the subscriber line because it is
isolated from it by a very high impedance and is simply connected
in parallel with the subscriber telephone set. It also does not
require a separate power supply as it draws power from the loop.
The detector circuitry may be installed without requiring
interruption of service since it has no direct electrical
connection to the telephone lines. In other words, the system of
the invention simply uses the telephone system as a convenient
transmission facility without cutting into it and without affecting
its normal operation. It may be noted that multiple replies on the
same question may be prevented simply by making the recharge time
of the incast signal generator circuitry longer than the replying
interval. Also, it is entirely possible to register a reply while
the telephone set is off-hook; however, the signal generator
circuit will not recharge as long as it is off-hook because the
current drawn by the telephone subset reduces the ring-to-tip
voltage to well below the voltage necessary to recharge it (48
volts).
An alternative mode of operation for the above-described system is
that of a true polling network. For example, it is known that a one
percent accuracy at the 50 percent confidence level may be achieved
by polling approximately twelve hundred people. Therefore, by
providing sufficient incast signal generators such that during a
particular poll there are responses available from 1,200 incasters,
a true polling network is achieved. To receive these replies, the
same number of detector circuits may be provided at the ratio of
one reply per detector. That is, one of the pairs in the cable
passing through the detector is associated with one incast signal
generator. In this way, it may be seen that the allocation of the
incast signal generator to subscribers may be changed from time to
time while retaining the same total number and without having to
relocate the detectors. Also, inferencing of the polling results is
possible because the identity and characteristics of the sources
are known.
The incasting system described herein may readily be adapted to
achieve a true polling network in combination with the interactive
participative broadcasting system as described above by providing
the participants of the true polling network with modified incast
signal generators which transmit coded incast reply signals. For
example, these signals may comprise a positive current pulse
followed a predetermined interval of time later by a negative
current pulse. The reply sorters associated with the participants
of the true polling network may also be readily adapted to
recognize the coded signals.
Of course, it should be realized that some of the concepts embodied
in the above-described incasting system may be adapted for use with
other than the telephone system. For example, a large auditorium
may be wired to simulate the telephone system with some or all of
the seats representing an incast source and the replies may be
detected using circuitry which performs an "OR" function thereon.
In this way, the economy associated with the detector circuitry of
applicant's invention is realized.
* * * * *